Regulatory Matters - MISO Return on Equity Complaints (Details) - FERC [Member]	Dec. 31, 2018
Loss Contingencies [Line Items]
FERC Authorized Return on Common Equity	10.32%
FERC Authorized Return on Equity Including Incentive Adder	10.82%
Return on Equity Complaint [Member]
Loss Contingencies [Line Items]
Proposed Return on Equity by Federal Administrative Law Judge	9.70%
Proposed Return on Equity by Federal Administrative Law Judge Including Incentive Adder	10.20%